“I am very sorry not to have been in Francfort when you were there at Mr. Albert’s, by whom I have been informed that you have purchased one of my newly-invented instruments (Telephons). Though I will do all in my power to give you the most ample explanations on the subject, I am sure that personal communication would have been preferable; specially as I was told, that you will show the apparatus at your next sientifical meeting and thus introduce the apparatus in your country. “Tunes[27] and sounds of any kind are only brought to our conception by the condensations and rarefactions of air or any other medium in which we may find ourselves. By every condensation the tympanum of our ear is pressed inwards, by every rarefaction it is pressed outward and thus the tympanum performs oscillations like a pendulum. The smaller or greater number of the oscillations made in a second gives us by help of the small bones in our ear and the auditory nerve the idea of a higher or lower tune. “It was no hard labour, either to imagine that any other membrane besides that of our ear, could be brought to make similar oscillations, if spanned in a proper manner and if taken in good proportions, or to make use of these oscillations for the interruption of a galvanic current. “However these were the principles wich (_sic_) guided me in my invention. They were sufficient to induce me to try the reproduction of tunes [_i.e._, tones--see footnote.--S. P. T.] at any distance. It would be long to relate all the fruitless attempts, I made, until I found out the proportions of the instrument and the necessary tension of the membrane. The apparatus you have bought, is now, what may be found most simple, and works without failling when arranged carefully in the following manner. “The apparatus consists of two separated parts; one for the singing station A, and the other for the hearing station B.[28] [Illustration: Fig 28.] “The apparatus A, a square box of wood, the cover of which shows the membrane (_c_) on the outside, under glass. In the middle of the latter is fixed a small platina plate to which a flattened copper wire is soldered on purpose to conduct the galvanic current. Within the cercle you will further remark two screws. One of them is terminated by a little pit in which you put a little drop of quiksilver; the other is pointed. The angle, which you find lying on the membrane, is to be placed according to the letters, with the little whole [hole] (_a_) on the point (_a_) the little platina foot (_b_) into the quicksilver screw, the other platina foot will then come on the platina plate in the middle of the membrane.